You've heard it here before: the only proven way to lose weight is to burn more calories than you eat. Specifically, for every pound you want to lose, you need to create a 3,500-calorie deficit. Sure you could slash that many calories from your weekly diet to make the digits on the scale drop by one each week, but that would mean you're just focusing on half of the calories in/calories out equation. If you want to be a really big loser (in terms of weight, that is), you also need to consider your daily calorie burn.

Yes, even if you're a regular runner, you may not be burning all the calories you can--or should--burn. In fact, the recently released Dietary Guidelines for Americans suggest that we all probably need to get more exercise. Aiming for 30 minutes of moderate activity most days of the week is no longer considered enough, especially if you're trying to lose weight or stave off age-related weight gain. Now the experts recommend 60 to 90 minutes of moderate- to vigorous-intensity exercise most days of the week. So, for the average runner looking to drop 10 pounds, a three-miler every other day just won't cut it.

While you probably don't have the time--or the endurance--to double your mileage in an effort to burn off that stubborn spare tire, there are several simple ways you can boost your caloric output to increase your weekly caloric deficit. Follow this three-step plan, designed by Wayne Westcott, Ph.D., the fitness research director at the South Shore YMCA, in Quincy, Massachusetts, to supercharge your running routine and turn your body into a calorie-burning machine.

Step 1Run Better

Since you're reading this magazine we'll assume you already run on a regular basis, which will definitely make your weight-loss efforts a lot easier. That's because running is one of the most efficient ways to burn calories. For every mile you log, you burn about 100 calories. At that rate, heaping on the mileage sounds like a pretty good way to torch a lot of calories. But that's not exactly the case. Adding a few extra miles will certainly help increase your calorie burn, but adding a ton of mileage is actually not the best way to boost your burn. "You might think that you should just double your miles and burn twice as many calories," says Westcott. "But the more you run, the more efficient your body gets at running." That means your body can get so used to running that you eventually burn fewer calories during each workout. And piling on the mileage also puts you at greater risk for injury.

So if the answer isn't adding lots of miles, what should you do? Try adding better miles--the kind of miles that have the power to significantly increase your caloric output. These better miles will challenge your body more than the miles you've been logging at the same steady pace, over the same terrain. And if you're working harder, you're burning more calories. If you're running four times a week, you can continue to do one or two steady-pace runs, but try adding these twists to your other runs.

Throw in speed bursts. Replace one of your steady-pace five-mile runs with one that's broken up into speed and recovery segments. If you usually cover the five-mile distance at a consistent nine-minute-per-mile pace, try this instead: Warm up, doing the first mile at a 10-minute pace. Pick up the pace for mile two, doing it in eight minutes. Slow down to a 10-minute recovery pace for mile three, pick it back up to an eight-minute pace for mile four, then end the run with another recovery-paced mile. "Just like a car, the body is less fuel-efficient at higher speeds," says Westcott. "You are still covering the distance, so you're not losing any endurance benefits, but you are gaining calorie-burning benefits."

Head for the hills. On another day, take your run up and over a few hills. Whenever your heart rate goes up, that's a sign that you're burning more calories, says Westcott. And any runner knows that one of the fastest ways to pump up your heart rate is to head uphill. Of course, what goes up, must come down--and downhill running can be more stressful on the muscles and joints. Westcott's advice is to examine your running routes and aim to always go up the steeper side of a hill (for the biggest cardio and calorie-burning boost) and run down the side with the more gradual grade.

Do a double. You probably look forward to the weekend when you have time for a long run. But you'll burn more calories out of the same miles if you break them up into two running sessions--one in the morning and one in the evening. "Doing two shorter bouts lets you increase the intensity, giving your body two opportunities to burn more calories," says Westcott.Step 2Cross-Train

Can't run another step? We have the solution: Increase your weekly calorie deficit by adding more nonrunning forms of exercise. At the top of the list, according to Westcott, should be circuit-training--a form of weight training designed to improve your strength, flexibility, endurance, and aerobic capacity. And all four of these benefits ensure that circuit-training is also a decent calorie burner.

It's called circuit-training because you complete a "circuit" of weight-training exercises, each working a different combination of the major muscle groups. The idea is to begin the workout with an aerobic warmup to get your heart rate up (10 minutes on a stair climber, elliptical trainer, or other cardio equipment). Then you move quickly from one exercise to the next to keep your heart rate up, completing the circuit as a continuous flow of activity. In other words, no standing around between exercises.

Aim for 10 to 12 exercises, hitting all parts of the body (two to three for arms, two to three for shoulders and chest, three to four for lower body, and three to four for abdominals and back). All of the exercises can be done on weight machines or with free weights, or a combination. Complete 10 to 15 repetitions of each move. "Instead of doing just eight reps at 80 percent of your one-lift maximum weight, do 15 reps at 65 percent of your max," suggests Westcott. "You'll end up lifting a higher volume overall, which will burn a few extra calories."

To increase the intensity of your circuit workout and boost your calorie burn, hop on any piece of cardio equipment for five minutes between every two or three exercises. A stationary bike provides an excellent cardio workout without putting stress on your joints, and it also uses muscles complementary to running

"Running tends to use more hamstring than quad strength, and on an upright cycle you focus more on quad strength," says Westcott. "So it's a very nice balance."

Of course, there are as many ways to cross-train as there are sports, so be creative. Swimming, kayaking, and rowing (whether on a boat or in a gym) all give your lower body a break from the pounding while providing you with a great upper-body and cardio workout. Hiking, while highly taxing on the lower body, has less impact than running and works the leg muscles in different ways.

Step 3Make Lifestyle Changes

Feel like your exercise calendar is all booked up? There are still several simple ways to add to your daily caloric deficit. And they're easy things you probably already know you should be doing--taking the stairs, carrying your own luggage through the airport, walking to people's offices rather than calling or e-mailing, parking farther away from stores. "I see people at the mall circling like vultures trying to get the closest parking space," says Westcott. "I not only save time by not circling, but I get a workout by walking the extra distance."

Make a conscious effort every day to increase the number of nonrunning steps you take. A five-mile run is equal to about 10,000 steps and 500 calories, but you can easily double that through daily activity. Wear a pedometer when you're not running and try to reach the goal of at least 10,000 steps per day.

One easy way to all but guarantee you hit the 10,000-step mark: Get a dog. A recent study at Northwestern Memorial Hospital revealed that when people got moving with their pets, both owners and dogs lost more weight and kept it off compared to people or pets that hit the road alone. And there's no rule that says it has to be your dog you're walking. Any dog will do, so reach out to family, friends, neighbors, or local shelters.

Finding an active hobby is another way to burn more calories each week. Think of options that are relaxing but not sedentary, such as gardening, golfing, sailing, or taking yoga. "Relaxing doesn't have to mean lying on the couch," says Westcott. "During your free time, don't just sit there, move!" The dividends of your calorie deficit will pay off big-time when you hit the scale.

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The Starting LineIf this looks like your current running schedule, check out the calendar below for some calorie-blasting improvements